Much activity has been devoted to avoiding the necessity of using on-floor conduits for conveying electrical power and communications lines to floor locations which were not within the original architectural and electrical planning of a facility, such as a multi-floor concrete building. Such on-floor conduits are unsightly and may pose a safety hazard, e.g., personnel may trip over the conduits and be injured.
One technique for avoiding the use of on-floor conduits involves the drilling of a passage through the concrete floor at a desired location and the routing of power or communications lines beneath the floor and then up through the passage. Transition apparatus known as "poke-throughs" have been developed for use in such passages. Such poke-throughs are subject to electrical and fire safety considerations. Among these are two fire-related requirements. First, the poke-through should not function as a chimney or fire-advancing flue in the event of a fire on the lower floor. Second, the poke-through should not function as a floor-to-floor heat conduction path.
These safety requirements have largely been met through the use of intumescent material. For example, co-assigned U.S. Pat. Nos. 5,003,127 and 5,107,072 disclose a poke-through assembly wherein a sheet of intumescent material is wired in place about a housing, and expands to fill and block the interfloor passage in the event of fire. Furthermore, thermally insulating materials have been interposed between metallic (and therefore heat conductive) portions of the poke-through devices. Thus, poke-through devices have come into common use.
With greater use of poke-through devices, there is, of course, interest in making their manufacturing economical, their installation easier and faster, and their retention more positive. One prior-art method requires the installer to turn two screws in order to cause a flat paddle to engage the side wall surface of the interfloor passage. Another method involves the use of a plurality of gripping fingers to provide self-anchoring, as disclosed, for example, in U.S. Pat. No. 4,770,643 to Castellani et al. Such fingers are angled so as to bend on insertion, but to resist subsequent pull-out of the poke-through. The devices with gripping fingers have the disadvantage of requiring a high insertion force in configurations that meet minimum pull-out force requirements. Further, they may take a permanent set (i.e., plastically deform) in use and thus not be reusable. The devices requiting the installer to mm fastening screws are undesirably labor-intensive. Further, prior art devices which require wrapping with a sheet of intumescent material are labor-intensive to manufacture.
There is, therefore, a need in the prior art for a poke-through electrical connection assembly which provides a self-anchoring retainer which meets minimum pull-out force requirements and yet has a low insertion force. The assembly and retainer should be re-usable, and the retainer should preferably be removable from the remainder of the assembly. Further, the intumescent material should be easy to apply during the manufacturing process.